George Dvorsky

Some earthquakes are so powerful they can actually be felt up in space. Looking to take advantage of this phenomenon, a group of researchers have created the world's first seismometer in orbit around the Earth. Well, to be more accurate, they're re-purposing a satellite originally designed to measure gravity fields on our planet's surface. It's likely a precursor to more powerful space-based stations that will help geologists monitor earthquakes — and even covert nuclear tests — as they happen.

It's called the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE), and it was launched into orbit by the European Space Agency in 2009. It's equipped with a highly sensitive gravity gradiometer which detects fine density differences in the crust and oceans of the Earth. It also has six accelerometers, which is what allows it to detect seismic disturbances.

Oh, and those thrusters you see in the above image — those are QinetiQ T5 ion thrusters that can be employed to adjust its orientation in low Earth orbit.

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GOCE has been used to probe hazardous volcanic regions and changing ocean conditions. And in fact, along with other satellite altimeters, it has been able to use its gravity-sniffing capabilities to measure sea surface height, which helps geologists and oceanographers track the direction and speed of geostrophic ocean currents.

But back in 2011, GOCE's monitoring team noticed that the satellite was able to detect the Tohoku earthquake in Japan. Essentially, the quake turned our planet into a giant subwoofer. The Earth was rung like a bell, causing it to transmit extreme low frequency subsonic seismic waves through the air and right into space.

During the Tohoku quake and the resultant tsunami - which together led to some 15,000 deaths - various instruments, including Global Positioning System satellites, detected ripples propagating in the electrons of the ionosphere, a layer of electrons and ions that overlaps with the ordinary, electrically neutral part of the atmosphere between 80–600 kilometres above Earth's surface.

The effect, picked up through delays in radio signals, suggested that the electrons were being pushed around by the neighbouring ions, which in turn were propagating an infrasound wave from the neutral atmosphere below...

..GOCE detected an acoustic wave of frequency 14 millihertz (mHz) about half an hour after the quake, and another at 6 mHz about an hour after. In effect, the detection makes GOCE the first orbiting seismometer.

In future, GOCE (or similar satellites) will monitor for earthquakes in remote places (like the middle of the ocean) and scan for nuclear tests (though a magnitude 3 may be quite difficult to detect). And indeed, only time will tell if GOCE will be able to pick up more subtle earthquake events than the one that struck Japan.